Generally, various irradiation methods of transmitting a proton beam generated by an accelerator such as a cyclotron or a synchrotron to a patient for radiotherapy using protons have been used. One of general proton beam transmission methods which are currently used most in proton-therapeutic institutions is a scattering mode in which a large therapeutic irradiation surface is formed by allowing protons to collide with a target of a certain material to be scattered. However, a therapeutic method using the scattering mode has several significant problems such as secondary radiation including neutrons and gamma rays generated while protons are scattered, activation of a brass shielder and a compensator formed of an acrylic material used for controlling an irradiation surface of radiation, an increase in unnecessary beam dose of a normal organ which occurs during a proton beam adjustment process using the compensator, etc.
To solve several the problems generated in the proton beam transmission method using the scattering mode, a proton therapy method using pencil beam scanning has been provided recently and will soon be utilized for patient care. The proton beam transmission method using a pencil beam scanning mode, unlike the conventional scattering mode transmission method, transmits several energy beam dose distributions to a patient for therapy using a combination of scanning magnets, and is the most advanced next generation therapeutic method capable of maximizing and optimizing cancer treatment using protons by facilitating intensity modulated proton therapy (IMPT) that has been impossible in the scattering mode. Also, since the pencil beam scanning method adjusts a beam using a combination of magnets, a scatterer and a shielder are unnecessary. Accordingly, side effects of the generation of secondary radiation caused by gamma rays and neutrons may be basically eliminated and time and cost for manufacturing a maximum of 30 or more shielders and compensators for each patient and each treatment area may be reduced.
In the proton beam transmission method using the pencil scanning mode described above, unlike a double scattering method of generating a flat beam using a lead scatterer and irradiating the same beam dose distribution, since a dose distribution includes a combination of a large number of pencil beams and an error occurs in a beam dose and a beam dose distribution transmitted to a patient when a position of one pencil beam changes, verification thereof is necessary. Particularly, there is a probability of the occurrence of an error in a moving organ. Accordingly, to reduce a dynamic uncertainty factor and to obtain an optimized treatment result, it is necessary to verify accuracy in a therapeutic beam dose of a therapeutic proton beam transmitted in a proton pencil beam scanning mode. That is, when a proton beam dose distribution and a therapeutic beam dose are not precisely determined in a human body, a therapeutic effect rapidly decreases or a beam dose is intensively transmitted even to tissue or an organ sensitive to radiation, thereby causing severe side effects to a patient.
Korean Patent Publication No. 10-2012-0085499, a prior document, discloses a conventional method of measuring a therapeutic proton beam dose. In the method of measuring a dose of a proton beam disclosed in the prior document, a beam dose is measured while optical fibers with different lengths are arranged in a water phantom while the water phantom is moving, and the method has a difficulty in being applied to measure a precise beam source position and beam dose distribution needed in a proton beam transmission method using a pencil beam scanning mode.
As described above, in the beam dose measurement in the proton-therapeutic method using a pencil beam scanning mode, unlike the conventional scattering mode, measurement using a three-dimensional water phantom is impossible and an apparatus for verifying a precise beam dose distribution has not yet been invented.